1. Field of the Invention
The present invention relates to a method of accurately measuring the temperature of an object on the basis of infrared rays incident upon an infrared sensor positioned behind a normally closed shutter.
2. Description of the Prior Art
A conventional method of measuring temperature is disclosed in, for example, Japanese Patent Application Publication No. Sho 62-503,119. In this method, a shutter is provided on a front side of an infrared sensor provided in a body case of a clinical thermometer with the condition that the shutter is always closed. To display a temperature, one output signal is obtained from the infrared sensor when the shutter is opened and closed by switching on a power source button and measuring a quantity of infrared rays from the output signal.
Although the above-described conventional method of measuring a temperature is remarkably simple in operation, the following disadvantages occur. As soon as the power source button is switched on, the infrared rays are incident upon the infrared sensor so that a peak of the signal output from the infrared sensor is unstable. Because the shutter is closed before the start of measurement, the sensing portion of the infrared sensor is under an equilibrium condition at a temperature within the body case. Thus, when the infrared rays are suddenly incident upon the sensing portion, the thermal-type infrared sensor is influenced by the room temperature as well as by the quantity of infrared rays. As a result, the first signal due to the infrared rays incident upon the sensor immediately after the shutter is opened is unstable relative to a second signal and signals thereafter. Consequently, it is difficult to measure temperature with high accuracy, for example, within .+-.0.01.degree. C. to 0.1.degree. C., with this conventional method of measuring a temperature.